Thermal interconnection for capacitor systems

ABSTRACT

Thermal protection is provided in systems utilizing high-current double-layer capacitors.

RELATED APPLICATIONS

This application is related to and claims priority from U.S. ProvisionalApplication No. 60/525,483 filed 26 Nov. 2003, Docket No. M111P, whichis commonly assigned and incorporated by reference; and

This application is related to and claims priority from U.S. ProvisionalApplication No. 60/518,422 filed 27 Nov. 2003, Docket No. M106P, whichis commonly assigned and incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is related to protection against heat in general,and to protection against heat effects in systems, using capacitors thatare capable of receiving or delivering high current.

BACKGROUND

Double-layer capacitors, which are also known as ultracapacitors andsupercapacitors, are now capable of being produced as individualcapacitor cells that can store hundreds and thousands of farads. Due inpart to their large capacitance, double-layer capacitors are capable ofsupplying or accepting large currents. However, single double-layercapacitor cells are limited by physics and chemistry to a maximumoperating voltage of about 4 volts, and nominally to about between 2.5to 3 volts. As higher capacitance capacitors are configured for use inincreasingly higher voltage applications, even higher currents may begenerated during charge and discharge of the capacitors. Future use ofdouble layer capacitors in high current applications will need toaddress this increase in heat.

SUMMARY

High capacitance capacitors can store large amounts of energy and arecapable of supplying or accepting large currents. As current flowthrough a capacitor increases, heat may be generated. Above a certainthreshold temperature or current, a capacitor may fail. The presentinvention addresses capacitor's tendency to fail at higher currentsand/or higher temperatures.

In one embodiment, a system comprises at least one double-layercapacitor; an interconnection, the interconnection coupled to the atleast one double-layer capacitor, the interconnection for carryingcapacitor current to or from the at least one double-layer capacitor,the interconnection functionally coupled to the at least onedouble-layer capacitor to reduce a temperature of the at least onedouble-layer capacitor. The interconnection may comprise a lowtemperature alloy. The interconnection may comprise a thermal fuse. Theinterconnection may comprise a thermal contactor. The at least onedouble-layer capacitor may comprise a first terminal and a secondterminal, wherein the thermal contactor is connected across the firstand the second terminal. Above a temperature the thermal contactor mayprovide a path with which to pass the current around the double-layercapacitor, wherein the temperature may be above about 85 degreesCelsius. The at least one double-layer capacitor may comprise a firstcapacitor and a second capacitor, wherein the thermal fuse is connectedbetween a first terminal of the first capacitor and a second terminal ofthe second capacitor, and wherein above a temperature the thermal fuseinterrupts the current between the first and the second terminal. Thetemperature may be reduced independent of the current. The temperaturemay be reduced based on a temperature external to the at least onedouble-layer capacitor. The interconnection may, comprise an increasedsurface area. The low temperature alloy may be selected from a groupconsisting of Bismuth-Lead, Tin, Cadmium, and Indium. The current maycomprise a current of at least 275 amps. The at least one double-layercapacitor may be coupled to an electrical device. The electrical devicemay be a vehicular electrical device. The electrical device may comprisean engine. The electrical device may comprise a propulsion engine. Thesystem may be utilized at a voltage above 40 volts. The system maycomprise a balancing circuit, wherein the first capacitor comprises athird terminal and the second capacitor comprises a fourth terminal, andwherein the balancing circuit is connected to the third and fourthterminal. The thermal fuse may comprise a bus bar. The system maycomprise a source of external heat removal. The source of external heatremoval may comprise a fluid, and wherein the at least one double-layercapacitor is immersed in the fluid. The fluid may be disposed in asealed container. The fluid may comprise an oil. The fluid may comprisean alcohol. The fluid may comprises a colored fluid. The current may bemore than 275 amps.

In one embodiment, a method of reducing a double-layer capacitortemperature comprises, the steps of providing one or more capacitor;coupling the one or more capacitor to an interconnection; passing acurrent through the interconnection; and using the interconnection toreduce a temperature of the capacitor as a function of a temperatureexternal to the double-layer capacitor. The interconnection may comprisea thermal contactor. The interconnection may comprise a thermal fuse.

In one embodiment, a capacitor-based system comprises a plurality ofinterconnected double-layer capacitors; and capacitor heat reductionmeans for reducing a temperature of the one or more interconnectedcapacitors.

Other embodiments, benefits, and advantages will become apparent upon afurther reading of the following Figures, Description, and Claims.

FIGURES

In FIG. 1 there are seen capacitors connected in series.

In FIG. 2 there are illustrated capacitor current vs. capacitortemperature curves.

In FIG. 3 there are seen interconnections provided with increasedsurface area.

In FIG. 4 there is seen a cell balancing circuit used with a circuitsubstrate.

In FIG. 5 there is seen a capacitor housing configured to provide anincreased surface area.

In FIG. 6 there are seen three transparent side views of six seriesinterconnected capacitors disposed within a container.

In FIGS. 7 a-b there is seen a thermal fuse used as an interconnectionbetween two capacitors.

In FIGS. 8 a-b there is seen use of a thermal contactor to bypasscurrent flow around a capacitor.

DESCRIPTION

High capacitance capacitors can store large amounts of energy and arecapable of supplying or accepting large currents. As current flowthrough a capacitor increases, heat may be generated. Above a certainthreshold temperature or current, a capacitor may fail. The presentinvention addresses the tendency of capacitors to fail at highercurrents and/or higher temperatures.

Referring now to FIG. 1, there are seen capacitors connected in series.In one embodiment, four 2600 F|2.5 V|60 mm×172 mm|525 g|sealedcapacitors 12, 14, 16, 18 are interconnected as a series string ofcapacitors. A type of Capacitor capable of such high capacitance isknown to those skilled in the art as a double-layer capacitor, oralternatively, as a supercapacitor or an ultracapacitor In FIG. 1, theseries string is formed using electrically conductive interconnections30. Interconnections 30 connect a negative terminal of a first capacitor12 to a positive terminal of a second capacitor 14, a negative terminalof the second capacitor to a positive terminal of a third capacitor 16,and a negative terminal of the third capacitor 16 to a positive terminal22 of a fourth capacitor 18. When a charging source 20 is connectedacross the positive terminal of capacitor 12 and the negative terminalof capacitor 18, a current flows through the capacitors and theinterconnections therebetween. In one embodiment, it has been identifiedthat when charged to 10 volts, over 2000, amps of instantaneous peakcurrent may flow through the capacitors 12, 14, 16, 18, andinterconnections 30, with such peak current dependent on the particularapplication. Accordingly, in one embodiment each capacitor 12, 14, 16,18 comprises terminals 12 a, 14 a, 16 a, 18 a, and interconnections 30that are sized to safely carry 2000 amps of peak current.

In FIG. 1 there is also seen that across respective positive andnegative terminals of the capacitor 12 and 14, and across respectivepositive and negative terminals of the capacitor 14 and 16, and, acrossrespective positive and negative terminals of the capacitor 16 and 18, arespective cell balancing circuit 32, 33, 35 is connected. A detaileddescription of connection; operation, and use of cell balancing circuitsis discussed in commonly assigned patent application Ser. No.10/423,708, filed 25 Apr. 2003, which is incorporated herein byreference. Because the current used by the cell balancing circuits 32,33, 35 is relatively small, the circuits and substrates that they may bemounted onto need not be as robust as the interconnections 30, but aswill be discussed in other embodiments later herein, a more robustsubstrate may nevertheless be desired. Ends of cell balancing circuits32, 33, 35 are connected to respective terminals of capacitors 12, 14,16, 18. Each cell balancing circuit 32, 33, 35 is also coupled by aconnection to a respective series interconnection 30, as is illustratedin FIG. 1.

Although capacitors comprising terminals disposed at opposing ends areillustrated in FIG. 1, it is understood that capacitors 12, 14, 16, 18could comprise other geometries, for example, with terminals that extendfrom the same end of a capacitor. It is therefore understood thatalternative embodiments may utilize interconnections 30 and balancingcircuits 32, 33, 35 that are coupled in a different orientation to thatshown by FIG. 1, and that such orientation and implementation is withinthe scope of the present invention. Furthermore, although only fourseries connected capacitors are illustrated in Figure, 1, the scope ofthe embodiments and inventions described herein envisions theinterconnection of less or more than four series connected capacitors.

Referring back to FIG. 2, and other Figures as needed, there isillustrated a capacitor current vs. capacitor temperature graph, whereina series interconnection 30 between the terminals of two 2600 F|2.5 V|60mm×172 mm cylinder|525 g|capacitors is formed by of one 0.5″ W×0.125″T×4.5″ L conductive bus bar interconnection. The uppermost curveillustrates that as capacitor current flow increases from 0 to about 275amps, about a 55 degree increase in capacitor temperature is observed.

Referring now to FIG. 3, and other Figures as needed, there are seeninterconnections provided, with increased surface area. Those skilled inthe art will identify that as current through the capacitors 12, 14, 16,18 increases, the temperature of the capacitors and interconnections 30through which the current flows may increase. It has been identifiedthat a reduction in the capacitor temperature may be achieved throughthe coupling of a sufficiently sized thermally conductive heatdissipater material against the capacitor in a manner that sinks anddissipates heat away from the capacitor.

In one embodiment, it has been identified that interconnections 30themselves can act as a heat dissipater. In one embodiment, eachinterconnection 30 is configured to comprise one or more increasedsurface area portion 30 a. In the context of the present invention, whatis meant by increased surface area (as opposed to minimized) is anysurface geometry with which improved heat dissipation may be achieved.For example, if a flat surface were considered as a being minimized insurface area, any protrusion or depression would act to increase thesurface area. Hence, in one embodiment, a flat rectangular bus bar typeinterconnection may be replaced with one that is dimensioned to includeone or more ribbed portion 30 a that provides an increased surface areawith which additional heat may be drawn and dissipated away from thecapacitors 12, 14, 16, 18. It is understood that although described andshown as ribs, an increased surface area could be provided by othergeometries, for example, wings, posts, curved areas, surface roughening,and others known and used by those skilled in the art.

Referring back to FIG. 2, and other Figures as needed, there isillustrated by a middle curve that, for a given temperature, two seriesinterconnected 2600 F|12.5 V|60 mm×172 mm cylinder|525 g|capacitors canbe operated at a higher current when connected in series by a bus barinterconnection that comprises an increased surface area geometry. Themiddle curve illustrates that as capacitor current flow increases from 0to about 350 amps, about a 55 degree increase in capacitor temperatureis observed. Series interconnections 30 between capacitors 12, 14, 16,18, may be thus configured with increased surface areas such that for agiven temperature the current that series interconnected capacitors maybe safely operated at may be increased. Similarly, seriesinterconnections 30 with increased surface areas facilitate that for agiven current, the operating temperature of a series interconnectedcapacitor may be reduced.

Referring again to FIG. 2, and other Figures as needed, there isillustrated by a bottommost curve, that at any given temperature, ascompared to the topmost curve and the middle curve, two seriesconnected, 2600 F|2.5 V|60 mm×172 mm cylinder|525 g|capacitors can beoperated at a higher current when used with an external source of heatremoval. The bottommost curve illustrates that as capacitor current flowincreases from 0 to about 475 amps, about a 55 degree increase incapacitor temperature is observed.

In one embodiment, an external source of heat removal comprises anairflow passing over and between the capacitors 12, 14, 16, 18, and theseries interconnections 30. The external source of heat removal can beused to further reduce the temperature, of the capacitors 12, 14, 16,18. By providing an external source of heat removal, series connectedcapacitors 12, 10 14, 16, 18 may be used at higher currents and/or lowertemperature in a wider range of applications and, with greaterreliability, than without external heat removal. It is identified thatwhen an external source of heat removal is used with an interconnection30 that comprises an increased surface area, further heat reduction maybe achieved. Although identified as an airflow, other external sourcesof heat removal may also be used and are within, the scope of thepresent invention. For example, external sources of heat removal may beprovided by immersion in, or exposure to, liquid, fluid, gas, or othermedium capable of safely acting to remove or dissipate, heat away fromthe interconnections 30 and/or capacitors 12, 14, 16, 18.

Referring now to FIG. 4, and other Figures as needed, there is seen acell balancing circuit 33 used with a circuit substrate. In oneembodiment, it is identified that each cell balancing circuit, forexample circuit 33, may be adapted to effectuate a further reduction inthe temperature of series interconnected capacitors, for example,capacitors 14, 16. In one embodiment, circuit 33 comprises one or morecircuit substrate portion 33 b. In one embodiment, circuit substrate 33b may comprise a thermally conductive material. In one embodiment,circuit substrate 33 b may comprise a thermally and electricallyconductive material. In one embodiment, wherein the circuit substrate 33b is electrically conductive, cell-balancing circuit 33 may beinsulatively coupled to substrate 33 b, for example, by an insulativeportion 33 c disposed therebetween.

In one embodiment a heat dissipation circuit substrate 33 b may comprisetwo or more electrically separated portions 33 d, 33 e, and/or 33 f. Inone embodiment, cell balancing circuit 33 may be thermally coupled toelectrically separated portions 33 d and 33 e and to terminals ofcapacitors 14 and 16, as follows: one portion of circuit 33 is coupledto portion 33 d, and a second portion of circuit 33 is coupled toportion 33 e. In this manner, an appropriately selected substrate 33 bmaterial, for example aluminum, can be used to draw heat away from thecapacitors 14 and 16 through the capacitor terminals of capacitors 33.In one embodiment, heat dissipation circuit substrate 33 b may compriseone or more increased surface area portion, for example, one or morerib, or the like.

Those skilled in the art will identify that thermal and/or electricalconnection of the heat dissipation substrate 33 b to the cell balancingcircuit 33, as well as to terminals of capacitors 14 and 16, would needto be made in a manner so as to not interfere with the electricaloperation of the capacitors and the circuit. For example, for each cellbalancing circuit 33, physical contact to, and electrical insulationfrom, each heat dissipation substrate may be effectuated by use of aninsulated portion between circuit and the heat dissipation substrate. Itis understood that other thermal and electrical connections andadaptations could be made without undue experimentation, and would bewithin the scope of one skilled in the art.

Referring now to FIG. 5, and other Figures as needed, there is seen acapacitor housing configured to provide an increased surface area. It isidentified that a capacitor 55 housing may also be adapted to effectuatereduction of the temperature of the capacitor. For example, in oneembodiment, a capacitor 55 may comprise one or more integrally formedincreased surface area portion, for example, one or more rib 55 b, orthe like. When used in combination with other embodiments describedherein, the increased surface area portions illustrated by FIG. 5 wouldallow for even more dissipation of heat away from the, capacitor 55.

Referring now to FIG. 6, and other Figures as needed, there are seenthree transparent side views of six series interconnected capacitorsdisposed within a container. In one embodiment, six series connectedcapacitors 81 may be disposed within a container 80. Although six seriesinterconnected capacitors are illustrated in FIG. 6, it is understoodthat the principles described herein could be extended to fewer or morecapacitors. For example, wherein 42 volts was a desired working voltage,those skilled in the art would identify that a larger number ofdouble-layer capacitors may need to be connected in series, for example,16 series interconnected 2.5 volt rated capacitors could be used toprovide about 42 volts. Similarly, higher or lower voltages can beprovided by providing more or less series connected capacitors. It isidentified, however, that dimensional requirements of the container 80may limit the configuration and potential use of one or more of the heatreduction principles and embodiments described herein. Accordingly, itis understood that one or more of the features described by previousembodiments described herein may or may not be able to be fully or evenpartially adapted for use within a container 80. For example, in oneembodiment, wherein there are six 2600 F|2.5 V|60 mm×172 mm cylinder|525g|capacitors interconnected by bus bars 30 and cell balancing circuits,to effectuate fitment in desired container dimensions, one or more ofthe bus bars 30, cell balancing circuit substrates, and capacitor 81housings may be configured with minimized or even no increased surfacearea portions.

In one embodiment, container 80 comprises a bottom portion 80 a and atop portion 80 b. In one embodiment, container 80 comprises a metal, orother material capable of resisting pressure. In one embodiment,container 80 comprises aluminum. In a manufacturing step, after one ormore interconnected capacitor 81 housing is disposed within thecontainer 80, a top portion 80 b and a bottom portion 80 a of thecontainer 80 may be sealed using sealing techniques such as edgecrimping, welding technique, soldering, or others known to those skilledin the art. Prior to sealing within the container 80, the one or morecapacitor 81 may be fixedly mounted within the container and coupled toone or more electrically conductive terminal connections 80 c. In oneembodiment, the container 80 comprises a sealable vent/fill portion 80d. Various vent/fill configurations are possible and are within theexpertise of those skilled in the art. If filled with a medium aftersealing of the container, it is identified that the vent/fill portion 80d may be used as the point of insertion of the medium.

In one embodiment, a container 80 with one or more interconnectedcapacitors 81 disposed within may be filled with a high thermalconductivity heat removal medium 85. In one embodiment, the heat removalmedium 85 comprises a fluid. Preferably, the heat removal medium 85 actsto direct or dissipate the heat away from the capacitors 81 andinterconnections 30 to the walls of the container 81, from which theheat may be subsequently dissipated to an external environment.

Although many fluids are capable of acting as a heat dissipater or heatremoval medium 85, it is identified that only some fluids may beappropriate for use with capacitors and embodiments described herein. Itis identified that heat removal medium 85 desirably exhibits highdielectric properties that do not present low resistance conductionpaths between the electrical connections and circuits used withincontainer 80, for example, between terminals of the capacitors 81 and/orterminals 80 c. It is also identified that heat removal medium 85desirably exhibits high flash point properties such that at hightemperatures the medium does not ignite. It is further identified that arelease of electrolyte from within a capacitor housing 81, as couldoccur when a capacitor that is subjected to excessive heat or current,could cause an undesired interaction with a heat removal medium in acontainer 80. Accordingly, it is identified that in one embodiment, aheat removal medium 85 desirably effectuates harmless mixing with anelectrolyte that may become present within the container 80. In oneembodiment, when an Acetronitrile (C2H3N) type of electrolyte is usedwithin a capacitor 81 housing, it is identified that release of theelectrolyte into a container 80 could cause undesired chemicalinteraction with an inappropriate heat removal medium 85. For example,because of low miscibility and high conductivity, water would beunsuitable as a heat removal medium, which either by itself or in thepresence of Acetonitrile electrolyte could electrolyze to create ahydrogen byproduct within container 80 that could subsequently explode.It is also identified that a heat removal medium 85 preferably minimizesthe potential for chemical and/or electrical interactions within acontainer 80, but as well, with an environment external to thecontainer. In one embodiment, a heat removal medium 85 that exhibits aplurality of the desired properties identified above comprises acommonly available type of cooking coil known as Wesson® Canola Oilavailable from ConAgra Foods Inc., One ConAgra Drive, Omaha, Nebr.68102.

A product comprising one or more sealed capacitor 81 housing disposedwithin a sealed container 80 may be provided for use in many differentapplications. For example, a sealed container 80 comprising one or moreinterconnected capacitor 81 disposed therein may be used as a primary orsecondary vehicular energy source. In one embodiment, conventionalbatteries in a hybrid vehicle may be replaced, by, or supplemented with,one or more sealed container 80. Because container 80 and the capacitors81 housed therein are sealed, the container 80 may be mounted in manymore physical orientations than that previously possible with lead acidbatteries. It has been identified that depending on the physicalorientation of a sealed container 80, the heat removal medium 85 maychange its orientation relative to the capacitors 81 housed therein.Because it is desired that a heat removal medium 85 preferably does notoccupy the entire free volume within the sealed container 80 (to providefor expansion of the medium at higher temperatures), when theorientation of the container is changed, the orientation of a heatremoval medium may also change such that one or mote of capacitorswithin the container may become exposed to a free volume of air.Exposure to a free volume, rather than a heat removal medium that candissipate heat away from a capacitor 81, may subject one or more of thecapacitors to increased or excessive heat build up. Accordingly, in oneembodiment, depending on the dimensional geometry of the container 80,and the geometry of the capacitors 81 disposed within, an appropriateamount of heat removal medium 85 is disposed within the container so asto take into account a range of potential usage orientations of thecontainer 80. Calculation of the amount of heat removal medium so that aremaining volume or air within the container 80 would allow forexpansion of the heat removal medium and, as well allow full orsubstantially full immersion of a particular geometry of interconnectedcapacitors within the heat removal medium over a particular usageorientation and temperature range, would vary according to dimensionalrequirements.

In one embodiment, it is identified that a container 80 andinterconnected capacitors 81 within can be configured such that whenpositioned or attached on a side, capacitors 81 disposed within thecontainer remain immersed within the heat removal medium. For example,in one embodiment, with a six sided box type container 80 and a properamount of heat removal medium 85, it is identified that the capacitors81 within the container may remain completely immersed in the heatremoval medium when the container is positioned on any one of the sixsides.

It is identified that despite implementation of one or more embodimentsdescribed herein, under some conditions, one or more capacitor 81disposed within a container 80 may nevertheless overheat and/or failsuch that the contents of the capacitor(s) may leak from within a sealedcapacitor 81 housing into the heat removal medium 85. It is desiredtherefore that the heat removal medium 85 within container 80 comprisesa high flash point and low chemical and/or electrical interactivity withthe particular contents of a capacitor 81 such interactions between theheat removal medium and the contents of the capacitors would preferablycreate only a benign pressure buildup within the container. One suchheat removal medium may comprise the aforementioned cooking oil.

In one embodiment, with an appropriately, sized and dimensionally sealedcontainer, a housing 80 may be configured to contain such the pressurebuild up. Alternatively, in one embodiment, a sealed vent/fill portion80 d may be provided to controllably release the pressure build up and,thus, some of the heat removal medium 85 within. Designs andconfigurations of vent/fill portions to controllably release pressure ata given pressure are numerous and could be implemented by those skilledin the art without undue experimentation.

It is identified that if the heat removal medium 85 is minimallyinteractive with an external environment, a release through a vent/fillportion may not be completely undesired. It is identified that release(via a pressure build up within container 80) of heat removal medium 85from within a container 80 may be used as an indication that overheatingor failure of a capacitor 81 has occurred or may occur. It is alsoidentified that it may be desired to more easily distinguish an expelledheat removal medium 85 from other medium present outside or near acontainer 80, for example, in a vehicular application where there mayalso be present expelled motor oil, transmission, radiator, and/or brakefluids. In one embodiment, it has been identified that by mixing theheat removal medium 85 with an inert or semi-inert material comprising adistinctive color or fragrance, the presence of the medium, and, thus,potential or actual failure of a capacitor within a container may beeasily identified. For, example, in one embodiment, a coloring agent maybe added to the heat removal medium 85 such that it differs fromstandardized colors of other fluids present in a vehicle. In oneembodiment, the coloring agent may comprise a color not used in themanufacture of motor oil, transmission, radiator, and/or brake fluids,for example, a blue coloring agent. Those skilled in the art willidentify that other colors used to indicate leakage of heat removalmedium 85 are also possible and within the scope of the presentinvention.

In one embodiment, it is identified that a heat removal medium 85 maycomprise an alcohol. In one embodiment, the alcohol comprises a methanolalcohol that may be mixed with a coloring agent. Methanol may findutility when, the container 80 is utilized in a low temperatureenvironment. However, it is identified that methanol may interact withelectrolyte and cause chemical interactions that could increase pressurewithin a container 80. Although interactions between heat removal medium85 and an electrolyte has been indicated as not being a preferredcondition, it is identified that the chemical properties of andinteraction with methanol may, be of a nature (i.e. non-explosive, etc.)enough that its pressurized expulsion from container 80 would notnecessarily be undesired.

A failure mode of a capacitor may be preceded by a temperature increaseat or near the capacitor. Such a temperature may be deemed to be below,above, or at the temperature that a capacitor may start to leakelectrolyte, and/or that a sealed container may begin to expel heatremoval medium. It is identified that devices other than capacitors mayalso generate heat, which may act increase, the temperature of acapacitors operating environment. In one embodiment, it is identifiedthat a nominal operating temperature of a capacitor and/or container isabout '40 to 85 degrees Celsius, and a failure mode temperature is about120 degrees. Celsius. Accordingly, it May be desired to take preventiveaction at some temperature, for example, before a failure modetemperature is reached or indicated.

Referring now to FIGS. 7 a-b, and other Figures as needed, there is seena thermal fuse. In one embodiment, it is identified that a conductivethermal fuse 90 may be used as an, interconnection between twointerconnected capacitors, for example, capacitors 91, 92. In oneembodiment, thermal fuse acts as a bus bar during periods that it isconductive. In one embodiment, a conductive thermal fuse 90 isconfigured to act at a certain predetermined environmental temperatureto be nonconductive. In one embodiment, a conductive thermal fuse 90 maycomprise two or more conductors 90 a-b held together in conductivecontact by an interconnection formed of a low melting point alloy 90 c.Those skilled in the art will identify that conductors 90 a-b as well aslow melting point alloy 90 c may comprise one or more surface area.Although surface areas in FIGS. 7 a-b ate illustrated as being more orless flat, it is identified that one or more of such surfaces maycomprise increased surface areas configured as previously describedherein.

It is identified that it may be desired that interconnections, forexample conductors 90 a-b, may be comprised of materials that minimizegalvanic effects that may be caused by use of dissimilar metals.Accordingly, if terminals 91 a, 92 a of respective capacitors 91, 92 arealuminum, in one embodiment the conductors 90 a-b are also aluminum.

It is further identified that one or more interconnection, for exampleconductors 90 a-b, preferably maintain geometry under pressure and/orhigh temperature, for example, as when pressed against a terminal 91 aor 92 a by a compression fitting, screw, bolt, and/or the like. Underhigh pressure connection forces, many materials are known to flow orchange their geometry. Those skilled in the art will identify that ifthe geometry of an interconnection changed under pressure, a resistivityat its connection points could be increased over time to an undesirablevalue such that heat would be generated, which in turn could increasethe temperature of capacitors 91 and 92. Accordingly, in one embodiment,an interconnection may comprise a high-grade aluminum that does not flowor change its geometry easily under pressure, for example, a 4047 gradeof aluminum, or other similar non-ductile metal.

Referring to FIG. 7 a, in one embodiment, thermal fuse 90 is configuredsuch that a portion of conductors 90 a, 90 b is fixedly connected torespective terminals 91 a, , 92 a. In one embodiment, respectiveseperatable end portions of conductors 90 a, 90 b are held inconductive, contact by a low melting point alloy 90 c. In oneembodiment, one or both of conductors 90 a, 90 b are springablypositioned so that they both make conductive contact. After and duringmaking of the contact, a low melting point alloy 90 c in a liquid orsemi-liquid state may applied at or near the contact point of theconductors 90 a, 90 b such that when the low melting point alloyhardens, the conductive contact between the conductors 90 a and 90 bformed by the low melting point alloy 90 c may be used to maintain apath for current to flow between capacitors 91 and 92.

Referring now to FIG. 7 b, in one embodiment, the conductors 90 a, 90 bare configured such that when not held in contact by the low meltingpoint alloy they do not make conductive contact. In one embodiment, thelow melting point alloy 90 c comprises a low melting point alloy of tinand bismuth. In one embodiment, a low melting point alloy 90 c is knownby those skilled in the art as “woods metal.” In other embodiments lowmelting point alloys may comprise other materials, for example,materials known as Cerro alloy, cerrolow, cerrosafe, cerroflow,cerromatrix, cerroseal, cerrobase, cerrotru, or cerrocast, cerrodent,one or more of which can comprise one or more of a Bismuth-Lead, Tin,Cadmium, Indium, and/or (Bi, Pb, Sn, Cd, In) alloy.

In one embodiment, thermal fuse 90 in a cross section may comprise asimilar width and height to that of previously discussedinterconnections 30. Accordingly, in one embodiment, thermal fuse 90 mayexhibit I²R heating effects that that are similar to that of aninterconnection 30. It is identified that these heating effects may besmall as compared to the heating effects of surrounding air or heatremoval medium fluid. Thus, at certain predetermined externalenvironmental temperature, the low temperature alloy 90 c may softensufficiently to allow the two conductors to springably separate and,thus, interrupt current flow passing between capacitors 91 and 92, aswell as any other interconnected capacitors that may be connected inseries. Thermal fuse 90 may be thus used to facilitate interruption incurrent flow independent of the current flow through the interconnection30. Those skilled in the art will identify that above a certaintemperature, even though a capacitor may not have failed, it may nolonger be as reliable. Accordingly thermal fuse 90 may be used to lowerthe temperature of capacitors by non-reversibly interrupting current sothat without some user intervention the current would not flow throughthe capacitors again.

In one embodiment, the alloy 90 c comprises a composition that maysoften enough so as to release the springable contact made by conductors90 a, 90 b when a safe upper, operating range of the capacitors 91, 92has been exceeded, for example, above 85 degrees Celsius. Theconstituent components of the low temperature alloy 90 c may be variedso as to soften or become liquid at other temperatures, and may be doneso by those skilled in the art without undo experimentation. Although nocontainer is shown in FIGS. 7 a-b, in one embodiment, one or morethermal fuse 90 may be used to form an interconnection betweencapacitors disposed within a fluid filled container. In such anembodiment, the thermal fuse could be used to interrupt current flowbased on a temperature of the fluid.

Referring now to FIGS. 8 a-b, there is seen use of a thermal contactor.In one embodiment, a conductive thermal contactor 95 is interconnectedacross a first and second terminal of a capacitor 96. When a capacitor96 begins to fail, or is anticipated to fail, for example as evidencedby an increased temperature of an external environment or external heatremoval medium around the capacitor, thermal contactor 95 may sense theincreased temperature and bypass current around the capacitor 96. It isidentified that in such a case, and wherein bypassed capacitor 96 ispart of a series string of interconnected capacitors, the maximumvoltage that may be applied across the series string of capacitors so asnot to exceed the series total of their voltage ratings would be reduced(by virtue of one or more less charged capacitor in the series string),but that one skilled in the art could over design such a series stringof capacitors to take into account that one or more capacitor may becomebypassed by a thermal contactor (for example, by adding extra capacitorsto a series string in anticipation of one or more capacitor in thestring failing).

Referring to FIG. 8 a, in one embodiment, thermal contactor 95 maycomprise at least two conductors 95 a, 95 b held in non-conductiveseparated opposition by a low melting point alloy 97. In one embodiment,the conductors 95 a, 95 b may comprise aluminum, copper, or other lowelectrically conductive material. In one embodiment, thermal contactor95 may be configured such that at least one conductor is attached to andis compressed against a spring, for example, a spring 95 c or 95 d.After and during compression of at least one spring by displacement ofone conductor against the spring, a low melting point alloy 97 in asoftened or liquid state may be applied at or near the conductor suchthat when the low melting point alloy hardens, the spring remains in acompressed condition, and such the conductor remains in a staticconfiguration, opposite to another conductor. In one embodiment, the lowmelting point alloy 97 comprises a low melting point alloy of tin andbismuth. In one embodiment, a low melting point alloy 97 is known bythose skilled in the art as “woods metal.” In other embodiments, lowmelting point alloys may comprise other materials, for example, amaterials known as Cerro alloy, cerrolow, cerrosafe, cerroflow,cerromatrix, cerroseal, cerrobase, cerrotru, or cerrocast, cerrodent,one or more of which can comprise one or more of a Bismuth-Lead, Tin,Cadmium, Indium, and/or (Bi, Pb, Sn, Cd, In) alloy.

Referring now to FIG. 8 b, at some predetermined temperature, forexample below 120 degrees Celsius, it is identified the low temperaturealloy 97 may soften sufficiently to allow one or both springs 95 c, 95 dto decompress and so as to force at least one conductor 95 a, 95 b tomove in a direction that allows a conductive contact to be made with anopposing conductor. With conductors 95 a and 95 b in conductive contact,instead of passing through the capacitor, current may pass around thecapacitor in the direction of the arrows shown in FIG. 8 b. Thoseskilled in the art will identify that in such a case, because no currentflow would occur through capacitor 96, its temperature would be lowered.In one embodiment, the thermal contact or may be configured to benon-reversible, with such properties being desired because once acertain temperature is reached, a double-layer capacitor could bedegraded in a manner that its further use would eventually cause itsfailure. Although no container is shown in FIGS. 8 a-b, in oneembodiment, one or more thermal contactor 95 may be used to form aninterconnection between capacitors disposed within a fluid filledcontainer. In such an embodiment, the thermal fuse could be used tobypass capacitor current flow based on a temperature of the fluid.

While the particular systems and methods herein shown and described indetail are fully capable of attaining the above described object of thisinvention, it is understood that the description and drawings presentedherein represent some, but not all, embodiments of the invention and aretherefore representative of the subject matter which is broadlycontemplated by the present invention. For example other dimensions,other form factors, other types of capacitors and other energy storagedevices could be adapted and used with one or more principles disclosedherein. Thus, the present invention should be limited by nothing otherthan the appended claims and their legal equivalents.

1. A method of reducing a double-layer capacitor temperature, comprisingthe steps of: providing one or more double-layer capacitor; coupling theone or more double-layer capacitor to an interconnection; passing acurrent through the interconnection and the double-layer capacitors; andusing the interconnection to reduce a temperature of the double-layercapacitors based on a temperature external to the double-layercapacitor.
 2. The method of claim 1, wherein the interconnectioncomprises a thermal contactor.
 3. The method of claim 1, wherein theinterconnection comprises a thermal fuse.